In recent years, there have been customer's demands for prints with increasing photographic image quality. In the existing photo-finishing laboratories, it is a common practice to obtain a large number of prints using automatic printers. However, since the humidity in the printer changes, for instance, according to the change in the atmospheric humidity from early morning to midday, the desired print quality is not obtained in some cases, due to color fluctuation in the finished print, when the sensitivity of the color printing paper is significantly affected by humidity change, which in turn can significantly affect productivity of the laboratory. This aspect poses a more difficult problem on "mini-labs", which have recently been common, since they are not air conditioned.
It is a well-known fact, published in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 20852/1990, that reciprocity law failure is improved by the silver halide emulsion described above, which comprises silver halide grains containing at least two compounds each containing one of the transition metals belonging to the groups II and V through VIII in the periodic table of elements.
Gold sensitization increases the sensitivity and improves the reciprocity law failure of silver halide emulsion, but it causes fogging.
Japanese Patent O.P.I. Publication Nos. 24246/1989 and 86135/1989 state that fogging can be suppressed by adding elemental sulfur upon chemical sensitization; however, this method proved to pause a problem of increased fluctuation of sensitivity upon humidity change (hereinafter referred to as humidity dependency), specifically a problem of significant deterioration over the humidity range from moderate to low humidities.